On Fri Mar 14, 2025 at 9:44 PM CET, Tamir Duberstein wrote: > On Fri, Mar 14, 2025 at 3:20 PM Benno Lossin <benno.lossin@xxxxxxxxx> wrote: >> >> On Fri Mar 7, 2025 at 10:58 PM CET, Tamir Duberstein wrote: >> > Implement `HasWork::work_container_of` in `impl_has_work!`, narrowing >> > the interface of `HasWork` and replacing pointer arithmetic with >> > `container_of!`. Remove the provided implementation of >> > `HasWork::get_work_offset` without replacement; an implementation is >> > already generated in `impl_has_work!`. Remove the `Self: Sized` bound on >> > `HasWork::work_container_of` which was apparently necessary to access >> > `OFFSET` as `OFFSET` no longer exists. >> > >> > A similar API change was discussed on the hrtimer series[1]. >> > >> > Link: https://lore.kernel.org/all/20250224-hrtimer-v3-v6-12-rc2-v9-1-5bd3bf0ce6cc@xxxxxxxxxx/ [1] >> > Signed-off-by: Tamir Duberstein <tamird@xxxxxxxxx> >> > --- >> > rust/kernel/workqueue.rs | 45 ++++++++++++--------------------------------- >> > 1 file changed, 12 insertions(+), 33 deletions(-) >> >> What is the motivation of this change? I didn't follow the discussion, >> so if you explained it there, it would be nice if you could also add it >> to this commit message. > > The motivation is right at the top: it narrows the interface and > replaces pointer arithmetic with an existing macro, and then deletes > unnecessary code. > >> > diff --git a/rust/kernel/workqueue.rs b/rust/kernel/workqueue.rs >> > index 0cd100d2aefb..0e2e0ecc58a6 100644 >> > --- a/rust/kernel/workqueue.rs >> > +++ b/rust/kernel/workqueue.rs >> > @@ -429,51 +429,23 @@ pub unsafe fn raw_get(ptr: *const Self) -> *mut bindings::work_struct { >> > /// >> > /// # Safety >> > /// >> > -/// The [`OFFSET`] constant must be the offset of a field in `Self` of type [`Work<T, ID>`]. The >> > -/// methods on this trait must have exactly the behavior that the definitions given below have. >> > +/// The methods on this trait must have exactly the behavior that the definitions given below have. >> > /// >> > /// [`impl_has_work!`]: crate::impl_has_work >> > -/// [`OFFSET`]: HasWork::OFFSET >> > pub unsafe trait HasWork<T, const ID: u64 = 0> { >> > - /// The offset of the [`Work<T, ID>`] field. >> > - const OFFSET: usize; >> > - >> > - /// Returns the offset of the [`Work<T, ID>`] field. >> > - /// >> > - /// This method exists because the [`OFFSET`] constant cannot be accessed if the type is not >> > - /// [`Sized`]. >> > - /// >> > - /// [`OFFSET`]: HasWork::OFFSET >> > - #[inline] >> > - fn get_work_offset(&self) -> usize { >> > - Self::OFFSET >> > - } >> > - >> > /// Returns a pointer to the [`Work<T, ID>`] field. >> > /// >> > /// # Safety >> > /// >> > /// The provided pointer must point at a valid struct of type `Self`. >> > - #[inline] >> > - unsafe fn raw_get_work(ptr: *mut Self) -> *mut Work<T, ID> { >> > - // SAFETY: The caller promises that the pointer is valid. >> > - unsafe { (ptr as *mut u8).add(Self::OFFSET) as *mut Work<T, ID> } >> > - } >> > + unsafe fn raw_get_work(ptr: *mut Self) -> *mut Work<T, ID>; >> > >> > /// Returns a pointer to the struct containing the [`Work<T, ID>`] field. >> > /// >> > /// # Safety >> > /// >> > /// The pointer must point at a [`Work<T, ID>`] field in a struct of type `Self`. >> > - #[inline] >> > - unsafe fn work_container_of(ptr: *mut Work<T, ID>) -> *mut Self >> > - where >> > - Self: Sized, >> >> This bound is required in order to allow the usage of `dyn HasWork` (ie >> object safety), so it should stay. >> >> Maybe add a comment explaining why it's there. > > I guess a doctest would be better, but I still don't understand why > the bound is needed. Sorry, can you cite something or explain in more > detail please? Here is a link: https://doc.rust-lang.org/reference/items/traits.html#dyn-compatibility But I realized that the trait wasn't object safe to begin with due to the `OFFSET` associated constant. So I'm not sure we need this. Alice, do you need `dyn HasWork`? --- Cheers, Benno
